Spring contact assembly

ABSTRACT

A spring contact assembly having a first plunger with a tail portion having a flat contact surface and a second plunger having a tail portion with a flat contact surface wherein the flat contact surfaces are overlapping and are surrounded by an external compression spring such that the sliding engagement of the flat surfaces increases during compression of the spring.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a Continuation of U.S. patent application Ser. No.12/206,659, filed Sep. 8, 2008, which claims priority to U.S.Provisional Patent Application Nos. 60/973,370, filed Sep. 18, 2007, and61/080,607, filed Jul. 14, 2008, the entire contents of which are herebyexpressly incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to electrical contact probes formingelectrical interconnects and, more particularly, to a spring contactassembly having two movable and overlapping plungers having flat contactsurfaces surrounded by an external spring.

BACKGROUND OF THE INVENTION

Conventional spring loaded contact probes generally include a movableplunger and a barrel having an open end for containing an enlargeddiameter section of the plunger, and a spring for biasing the travel ofthe plunger in the barrel. The plunger bearing slidably engages theinner surface of the barrel. The enlarged bearing section is retained inthe barrel by a crimp near the barrel open end. The plunger is commonlybiased outwardly, a selected distance by the spring and may be biased ordepressed inwardly into the barrel, a selected distance, under forcedirected against the spring. Axial and side biasing of the plungeragainst the barrel prevents false opens or intermittent points of nocontact between the plunger and the barrel. The plunger generally issolid and includes a head or tip for contacting electrical devices undertest. The barrel may also include a tip opposite the barrel's open end.

The barrel, plunger and tips form an electrical interconnect between theelectrical device under test and test equipment and as such, aremanufactured from an electrically conductive material. Typically theprobes are fitted into cavities formed through the thickness of a testplate or socket. Generally a contact side of the electrical device to betested, such as an integrated circuit, is brought into pressure contactwith the tips of the plungers protruding through one side of the testplate or test socket for manufacturing spring pressure against theelectrical device. A contact plate connected to the test equipment isbrought to contact with the tips of the plungers protruding from theother side of the test plate or test socket. The test equipmenttransmits signals to the contact plate from where they are transmittedthrough the test probe interconnects to the device being tested. Afterthe electrical device has been tested, the pressure exerted by thespring probes is released and the device is removed from contact withthe tip of each probe.

The process of making conventional spring probes involves separatelyproducing the compression spring, the barrel and the plunger. Thecompression spring is wound and heat treated to produce a spring of aprecise size and of a controlled spring force. The plunger is typicallyturned on a lathe and heat treated. The barrels are also sometimes heattreated. The barrels can be formed in a lathe or by a deep draw process.All components may be subjected to a plating process to enhanceconductivity. The spring probe components are assembled either manuallyor by an automated process.

An important aspect of testing integrated circuits is that they aretested under high frequencies. As such impedance matching is requiredbetween the test equipment and the integrated circuit so as to avoidattenuation of the high frequency signals. Considering that spacingwithin a test socket is minimal, in order to avoid attenuation of thehigh frequency signals, the length of the electrical interconnect formedby the probes must be kept to a minimum. To address this problemexternal spring probes have been developed having a shorter length thanconventional probes. External spring probes consist of two separatesections each having a tip and a flange. A contact component extendsfrom each probe section opposite the tip. The two contact componentscontact each other and the spring is sandwiched between two flanges thatsurround the contact components. Typically the first contact componentis a barrel while the second contact component is a bearing surface. Thebearing surface is slidably engaged to the inner surface of the barrel.These probes are fitted into cavities formed in the test sockets usedduring testing. A problem associated with these type of external springprobes is the expense to manufacture due to costly machining operations.

In response thereto external spring probes were designed having flatcomponents which can be produced less expensively by stamping. Typicallythese designs incorporate two components which are connectedorthogonally and the electrical path between the two components isthrough a protruding end surface. A problem with this design is that thecomponents wear out rather quickly and have a short life span requiringconstant replacement.

Consequently a need exists for a new spring contact assembly design thatis less expensive to manufacture.

SUMMARY OF THE INVENTION

The present invention is directed to a spring contact assembly havingtwo movable and overlapping contact members or plungers surrounded by anexternal spring. Each plunger has a contact portion and a tail portionwherein the tail portion has a flat surface that passes over and makescontact with an opposing plunger tail portion inside the spring whenassembled. The spring has end coils that press onto each of the opposingplungers to prevent the plungers from separating from the spring, thusfixing the plunger contact portion and the tail portions with respect toeach end of the spring. Utilizing the natural torsional movement of thespring while it is compressed, the flat surfaces of the plunger tailportions maintain contact throughout the compression stroke of thecontact assembly. The contact between the opposing flat sectionsprevents the twisting or torsional movement of the spring fromtranslating to the tips on the contact portions. The opposition to thenatural twisting enhances the electrical conductivity of the components,which in turn improves performance of the spring contact assembly. Thespring can also have reduced diameter coil sections along the length ofthe spring to further constrain the plunger tails and enhance theinteraction between the two plungers, or further biasing effect can becreated by adding an offset coil section in the spring.

The flat surface on the tail portion of the plunger would normally beformed parallel at the midline of the cylindrical tail portion diameterfor each plunger. In an alternative embodiment, the flat surface may beformed parallel above the midline of the cylindrical tail diameter toincrease the resulting combined thickness of the assembly, creatingadditional interaction between the two plungers. In further embodimentsthe flat surface on the tail portion may be formed at either an angle toor in a helix about the midline of the cylindrical tail portiondiameter.

In yet another embodiment, one plunger includes an essentially flat tailportion, centrally located along the axis of the component, and theopposite plunger has a mating slot which receives the flat tail portionof the opposite plunger. This design allows for two edges to be inslidable contact engagement, thus enhancing resistance performance.

Each of the plungers may be formed in a general cylindrical shape,suitable for lathe, screw machine or other similar manufacturingequipment. Alternatively the plunger may be formed in a generally flatshape, suitable for stamping, etching, photolithography or other similarmanufacturing technique for creating substantially two dimensionalgeometries.

For generally flat shaped plungers, the plunger tail section may have aportion that extends beyond the opposite ends of the coils of thespring. This facilitates enhanced electrical contact and adds additionalsupport to the opposite plunger tip or contact portion. The plunger tailportion that extends past the opposite end of the spring can have theedges on one side reduced to provide for maximum material utilization. Aslot may also be provided in the spring interference area of the flatpattern version of the plunger to provide additional compliance,absorbing tolerance while providing a reliable press fit. Flat plungerdesigns also can benefit from having the plungers generally slidingtogether at an inclined configuration, thus transferring some of theaxial forces supplied by the external helical spring to a perpendiculardirection, which is normal to, mating plunger surfaces. This normalsurface force enhances intimate electrical contact between thecomponents. Methods for maintaining the probe together include enlargedtail portions extending past reduced diameter center coils andinterlocking tabs on the contact portions. Kelvin configurations arealso possible having two separate electrical paths isolated from oneanother within a single probe.

Further benefits provided by flat geometry allow multiple plungers to beeasily fabricated as part of a lead frame assembly, facilitating platingand assembly in high volumes. Completed assemblies can also be suppliedattached to a lead frame, making it easier for the end user to load theprobe assembly into a finished test fixture or socket. Tipconfigurations can be single point, multiple point or three dimensional.

The present invention also contemplates a spring contact assembly havinga cylindrical plunger in combination with a flat plunger. This hybridcombination can provide for cylindrical tip geometries to addresssufficient testing for solder ball or other geometries while reducingthe manufacturing costs for a fully cylindrical contact assembly byincorporating a flat plunger as the opposite plunger. These and otheraspects of the present invention will be more fully understood withreference to the detailed description in combination with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the spring contact assembly of thepresent invention;

FIG. 2 is a side view of a first plunger of the spring contact assemblyof FIG. 1;

FIG. 3 is a side view of an alternative plunger design of the presentinvention;

FIG. 4 is a side view of a second plunger of the spring contact assemblyof FIG. 1;

FIG. 5 is a side view of a spring of the spring contact assembly of FIG.1;

FIG. 6 is a cross-sectional view of the spring contact assembly of FIG.1;

FIG. 7 is a side view of an alternative plunger design of the presentinvention;

FIG. 8 is a side view of an alternative plunger design of the presentinvention;

FIG. 9 is an axial cross-sectional view of the spring contact assemblyof FIG. 1 inserted into a test socket;

FIG. 10 is a perspective of an alternative embodiment spring contactassembly of the present invention;

FIG. 11 is a side view of one plunger of the spring contact assembly ofFIG. 10;

FIG. 12 is a schematic illustration of a stamping procedure for theplunger of FIG. 11;

FIG. 13 is a side view of a second plunger of the spring contactassembly of FIG. 10;

FIG. 14 is a cross-sectional view of the spring contact assembly of FIG.10;

FIG. 15 is an axial cross-sectional view of an alternative springcontact assembly of FIG. 10;

FIG. 16 is a perspective view of an alternative spring contact assemblyof the present invention;

FIG. 17 is a perspective view of another alternative embodiment springcontact assembly of the present invention;

FIG. 18 is a side view of another alternative embodiment spring contactassembly of the present invention;

FIG. 19 is a perspective view of another alternative embodiment springcontact assembly of the present invention;

FIG. 20 is a perspective view of another alternative embodiment springcontact assembly of the present invention;

FIG. 21 is a perspective view of another alternative embodiment Kelvinmeasurement spring contact assembly of the present invention;

FIG. 22 is a perspective view of three dimensional contact tipembodiment of the present invention;

FIG. 23 is a perspective view of a spring contact assembly with the tipconfiguration of FIG. 22.

FIG. 24 is a perspective view of an alternative contact tip design ofthe present invention;

FIG. 25 is a perspective view of FIG. 24 illustrating a threedimensional contact tip;

FIG. 26 is a perspective view of an alternative contact tip design; and

FIG. 27 is a perspective view of FIG. 26 illustrating a threedimensional contact tip.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-11 illustrate a first embodiment spring contact assembly 10 ofthe present invention. The spring contact assembly 10 includes a firstcontact member or plunger 12, a second contact member or plunger 14, anda spring 16. As shown in FIG. 2, plunger 12 includes a contact portion18 and a tail portion 20. A contact tip 22 is positioned at an end ofthe contact portion 18 and can have multiple contact geometries as alsoshown in FIG. 3 and FIG. 4. A flange 24 is positioned between contactportion or section 18 and tail portion or section 20. Flange 24 has aflat face 26 used for aligning the probe during assembly. The plungertail portion 20 has a cylindrical surface 28 and a flat surface 30extending along its length.

Plunger 14 as shown in FIG. 4 also includes a contact portion or section32 and a tail portion or section 34. A flange 36 is positioned betweencontact section 32 and tail section 34 and also includes a flat surface38 for positioning plunger 14 during assembly. Tail section 34 has acylindrical surface 40 and a flat surface 42 extending along its length.Flat surfaces 30 and 42 pass over one another and make contact inside ofspring 16 when assembled, as also seen in FIG. 9. Flat surfaces 30 and42 increasingly engage one another during compression of the assembly.

As shown in FIG. 5 the spring 16 has end coils 44 and 46 at oppositeends of the spring that press onto plunger tail sections 20 and 34 atcylindrical sections 48 and 50 adjacent flanges 24 and 36. The end coils44 and 46 have a slightly smaller diameter and therefore firmly gripcylindrical sections 48 and 50 to prevent the plungers from separatingfrom the spring, thus fixing the plunger tips 22 and 52 and flatsurfaces 30 and 42 with respect to each spring end. Utilizing thenatural torsional movement of the spring 16 while it is compressed, theflat portions 30 and 42 of the plungers maintain contact throughout theentire stroke of the probe as also shown in FIG. 6. The contact betweenthe opposing flat sections prevents twisting or torsional movement fromtranslating it to the spring contact tips 22 and 52. The opposition tothe natural twisting enhances the electrical conductivity of thecomponents, which in turn improves the performance of the contact.

The flat section 30 as shown in FIGS. 2 and 3 can be formed parallel atthe midline of the cylindrical tail portion diameter for each plunger orthe flat section 42 may be formed parallel above the midline 54 of thecylindrical tail diameter for each plunger as shown in FIG. 4 toincrease the resulting combined thickness of the assembly, creatingadditional interaction between two plungers in an assembly. AlthoughFIGS. 1-4 show three different plunger tip designs, it is to beunderstood that any plunger tip design could be utilized depending uponits particular application. To further constrain the tail sections 20and 34 and enhance the interaction between the two plungers, the spring16 can employ reduced coil sections 56 as shown in FIG. 5. Furtherbiasing effect can also be created by offsetting coil sections 56.

Alternative designs for the plunger tail section can include the flatsurface 58 formed in a helix about the midline of the cylindrical taildiameter as shown in FIG. 7 or the flat section 60 may be formed at anangle to the midline of the cylindrical tail diameter as shown in FIG.8. As with all of the various plunger designs, the tail section may havea reduced end section 62 that allows the spring to be threaded onto thetail portion before being press fit on the reduced diameter sectionadjacent the flange. The reduced section 62 allows the plunger to pilotinto the spring, easing the assembly process. As previously indicated,the cylindrical sections 48 and 50 of the plunger tails creates aninterference fit with the end coils of the spring and the gripping forcecreated between the cylindrical sections and the end coils is sufficientto keep the assembly together during normal handling and use and incombination with the flat surfaces resist normal torsional forcesapplied by the spring. The generally cylindrical plunger designs ofFIGS. 1-9 are manufactured by machinings such as a lathe, screw machineor other similar manufacturing equipment.

An alternative spring contact assembly 70 is illustrated in FIGS. 10-15.Spring contact assembly 70 includes two movable and overlapping plungers72 and 74 surrounded by an external spring 76. Plungers 72 and 74 areformed in a generally flat shape, suitable for stamping, etching,photolithography or other similar manufacturing technique for creatingsubstantially two-dimensional geometries as generally referenced as 78in FIG. 12. An additional benefit of flat plunger geometry allowsmultiple plungers to be easily fabricated as a part of a lead frameassembly, facilitating plating and assembly in high volume. Completedassemblies can also be supplied attached to a lead frame, making iteasier for the end user to load the probe assembly into a finished testfixture or socket 110 (shown in FIG. 9).

Plunger 72 includes a contact portion or section 80 and a tail portionor section 82. Contact section 80 includes a contact tip 84 which can beany of a number of geometrical configurations. Considering the entireplunger has a flat configuration, plunger tail section 82 includes aflat surface 86. A flange 88 is positioned between contact section 80and tail section 82. Tail section 82 includes an enlarged portion 90 forcreating an interference fit with end coils of the spring 76 to retainthe spring contact in its assembled configuration. Mating plunger 74also includes a contact portion or section 92, a tail portion or section94, and a flange 96 positioned between the contact section and tailsection. Tail section 94 includes an enlarged portion 98 for creating aninterference fit with the end coils of spring 76.

In the flat configuration spring contact assembly 70, the plunger tailsections 82 and 94 may have an end portion 100 that extends past the endcoils of the spring as shown in FIG. 10. This design enhances theelectrical contact between the plungers and adds support to the oppositeplunger tip. One or both of the plunger tails can extend beyond the endcoils for a particular application. As shown in FIG. 11 and FIG. 14 theend portion 82 which may extend beyond the end coils of the spring mayhave the corner edges 102 removed allowing for maximum materialutilization.

As shown in FIG. 13 plunger 74 may include a slot 106 in the springinterference area of the plunger to provide additional compliance,absorbing tolerance while providing a reliable press fit for the endcoil. As shown in FIG. 15 the flat plunger design benefits from the newresult of having the plungers 72 and 74 generally sliding together in aninclined configuration with respect to a midline axis 108. The plungerssliding together at an incline configuration transfers some of the axialforces supplied by the external helical spring 76 to a perpendiculardirection, or normal to, the mating flat plunger surfaces. The normalforce enhances intimate electrical contact between the plungers as shownin FIG. 15.

Yet another alternative embodiment spring contact assembly 112 is shownin FIG. 16 comprising mating plungers 114 and 116 and an externalhelical spring 118. In this configuration, plunger 114 has a flat tailportion 120 and plunger 116 has a tail portion 122 having a feature withinternally opposed flat surfaces 124 for receipt of flat tail 120. Tailportion 120 is centrally located along the axis of plunger 114 and thefeature 124 is centrally located along the axis of plunger 116. Springcontact assembly 112 allows for two flat edges 126 and 128 to bereceived in slidable contact with flat edges within feature 124. Thisdesign provides for enhances resistance performance of the springcontact assembly.

FIG. 17 illustrates yet another alternative embodiment spring contactassembly 130 which is a hybrid combination of the spring contactassemblies of FIGS. 1 and 10. Spring contact assembly 130 has acylindrical plunger 132 and a flat plunger 134 in slidable contactwithin an external helical spring 136. Tail portion 138 of plunger 132has a flat surface 140, and tail portion 142 of plunger 134 also has amating flat surface 144. Flat surfaces 140 and 144 are in slidableengagement.

FIG. 18 illustrates another alternative embodiment spring contactassembly 146 of the present invention. The spring contact assembly 146is a flat configuration having a first contact member 148 and a secondcontact member 150. Each of the tail portions 152 and 154 of contactmembers 148 and 150 include an enlarged tail section 156 and 158 whichpass through reduced diameter center coil sections 160 of helical spring162. The enlarged tail portions are opposite contact tips 164 and 166 ofeach contact member. The enlarged tail section passes through thereduced diameter coils and the force of the spring is sufficiently lowsuch that the contact members do not disengage from the spring.

FIG. 19 illustrates another alternative embodiment spring contactassembly 168 which illustrates another alternative method for retainingcontact members 170 and 172 to helical spring 174. In this embodiment,the center sections 176 and 178 of tail portions 180 and 182respectively, are pierced through forming a tab 184, 186, which whencontact members 170 and 172 are assembled within the spring 174, thetabs interlock.

FIG. 20 illustrates another alternative spring contact assembly 188which illustrates another alternative for connecting the contactmembers. Assembly 188 includes a first contact member 190 and a secondcontact member 192 having tail portions 194 and 196 positioned within ahelical spring 198. The center section 200 and 202 of the tail portionshave a non-centered tab 204 and 206 which when assembled interlock. Tabs204, 206 are formed by a forming or folding operation.

FIG. 21 illustrates yet another alternative embodiment spring contactassembly 208 which is a Kelvin measurement configuration. Assembly 208has two separate electrical paths within a single spring 210. This isaccomplished by having two separate contact members 212 and 214 adjacentone another. Members 212 and 214 are electrically isolated from eachother and from spring 210 by having a non-conductive coating positionedupon adjacent surfaces. Contact member 212 has a first contact segment216 and a second contact segment 218. Similarly, contact member 214 hasa first contact segment 220 and a second contact segment 222. Each ofsegments 216 through 222 have a tail portion 224, 226, 228 and 230,respectively. Tail portions 224, 226, 228 and 230 have conductivesurfaces 232 such that only sections 224 and 226 electricallycommunicate with one another and only sections 228 and 230 electricallycommunicate with one another. Tail sections 224 through 230 arepositioned within spring 210. Assembly 208 has two separate electricalpaths within a single spring wherein each contact path consists of twoslidably engaging tail portions and each contact path is electricallyisolated from its neighboring contact path.

FIGS. 22 and 23 disclose another alternative embodiment spring contactassembly 234 having a first contact member 236 and a second contactmember 238. Contact member 236 includes sections 240 and 242 each havinga slot 244 so that sections 240 and 242 can engage one another to createa three dimensional contact tip 246. Contact tip 246 comprises fourcontact points 248. Sections 240 and 242 are illustrated as beingconnected perpendicularly, however, it is to be understood that slots244 can be machined such that the two sections can be assembled at anangle other than perpendicular. Contact section 236 and contact section238 have tail portions 250 and 252 which are positioned within spring254.

FIGS. 24 and 25 illustrate an alternative embodiment three dimensionalcontact tip configuration. Contact member 256 includes a tail portion258 and a contact tip portion 260. Contact member 256 is a flatconfiguration as shown in FIG. 24 and contact tip 260 can have a threedimensional configuration as shown in FIG. 25 by bending or otherwisedeforming the flat contact tip into a three dimensional shape. It is tobe understood that the contact tip configuration although illustratedwith three contact points 262, 264 and 266 can have any number ofcontact points depending upon the particular application. The tipgeometry can be V-shaped, U-Shaped or other shapes to transform anotherwise two dimensional contact tip into a three dimensional contacttip. This can be done by bending or other forming type operations.Similarly, FIGS. 26 and 27 illustrate yet another alternative threedimensional contact tip design for contact member 268. Contact member268 initially is formed in a flat two dimensional configuration as shownin FIG. 26 wherein contact member 268 includes a tail portion 270 and acontact tip portion 272. As shown in FIG. 27, contact tip portion 272 isfolded upon itself to form the three dimensional configuration. In thisembodiment, four contact points 274, 276, 278 and 280 are illustrated.

Although the present invention has been described and illustrated withrespect to several embodiments thereof it is to be understood thatchanges and modifications can be made therein which are within the fullscope of the invention as hereinafter claimed.

1. A spring contact assembly comprising: a first contact member having atail portion having a flat contact surface along a length of the tailportion and a flange having means for aligning the first contact memberadjacent the tail portion; a second contact member having a tail portionhaving a flat contact surface along a length of the tail portion; and acompression spring attached to the first contact member tail portion andthe second contact member tail portion, whereby the flat contact surfaceof the tail portion of the first contact member slidably engages theflat contact surface of the tail portion of the second contact memberand increases in contact surface area of the flat surfaces duringcompression of the spring to overcome a torsional spring force on thefirst contact member and the second contact member.
 2. The assembly ofclaim 1 wherein the spring includes reduced diameter end coils whichengage the tail portions.
 3. The assembly of claim 1 wherein the springincludes reduced diameter coil sections which engage the tail portions.4. The assembly of claim 1 wherein as least one of the first contactmember and the second contact member is cylindrical.
 5. The assembly ofclaim 4 wherein both the first contact member and the second contactmember is cylindrical and the second contact member has a flange havingmeans for aligning the second contact member adjacent the tail portion.6. The assembly of claim 1 wherein at least one of the first contactmember and the second contact member is a flat configuration.
 7. Aspring contact assembly comprising: a first flat contact member having acontact tip and a tail portion having a contact surface along a lengthof the tail portion; a second flat contact member having a contact tipand a tail portion having a contact surface along a length of the tailportion; and a compression spring attached to the first flat contactmember tail portion and the second flat contact member tail portion,whereby the contact surface of the tail portion of the first flatcontact member slidably engages the flat contact surface of the tailportion of the second flat contact member during compression of the andwhereby the contact tip of the first flat contact member is offsetaxially from the contact tip of the second flat contact member.
 8. Theassembly of claim 7 wherein the spring includes reduced diameter endcoils which engage the tail portions.
 9. The assembly of claim 7 whereinthe spring includes reduced diameter center coils which engage the tailportions.
 10. The assembly of claim 7 wherein an end portion of the tailportions of the first or second contact members extend beyond an endcoil of the compression spring when the contact assembly is compressed.11. The assembly of claim 7 wherein an edge surface of the tail portionis removed.
 12. The assembly of claim 7 wherein the tail portions haveinterlocking tabs.
 13. The assembly of claim 7 wherein the first contactmember has a three dimensional contact tip.
 14. The assembly of claim 13wherein the contact tip of at least one of the first flat contact memberor the second flat contact member comprises a first tip section have aslot and a second tip section having a slot such that each slot engagesone another perpendicularly to create the three dimensional contact tip.15. The assembly of claim 13 wherein the contact tip is threedimensional by being folded upon itself.
 16. A flat contact memberhaving a contact tip portion and a tail portion opposite the contact tipportion wherein the contact tip portion is three dimensional.
 17. A flatcontact member of claim 16 wherein the tip portion comprises a first tipsection having a slot and a second tip section having a slot whereby theslots engage one another perpendicularly.
 18. The flat contact member ofclaim 16 whereby the contact tip portion is three dimensional by beingfolded upon itself.